Introduction: There are two common methods for inserting pedicle screws, having different entry points: a straight forward approach using Roy Camille’s entry point and a trajectory involving a lateral entry point. With both techniques, the screws are ideally confined completely within bone inside the pedicle. The objective of this study was to analyze the biomechanical differences between the two trajectories using bilateral pullout testing and human cadaveric vertebrae, with and without an interconnecting crosslink.
Methods: 62 individual lumbar vertebrae were dissected, disarticulated, potted and instrumented using appropriately sized pedicle screws. The specimens were divided into two groups according to the trajectory used (S-straight and L-lateral) with further subdivision into groups receiving a crosslink (CL) or not (no CL). Screws were pulled out bilaterally, in a dorsal direction, while recording load vs. displacement.
Results: The mean (±one stdev) maximum pullout loads are shown in Fig. 1.) The differences in pullout between S and L, with or without a crosslink were not significant (p>0.4). The mean pullout load was greater with a crosslink vs. no crosslink for both S (p=0.23) and L (p=0.04). There were more unilateral failures in cases without a crosslink (S and L), and the mean pullout load with unilateral failures (S and L) was greater with a crosslink than without (p<0.001). Multiple regression analysis did not show significant relationships between pullout, BMD, screw angle, %Fill-Pedicle or %Fill-Length, for individual sub-groups of screw trajectory and presence of crosslink. However, disregarding S, L and CL, pullout load could be predicted by age, BMD and %Fill of the screw (p<0.001).
Conclusions: Based on dorsally directed pullout tests, there were no differences between S and L, with or without a crosslink. However, the addition of a crosslink increased the resistance to pullout by 60% (L, p=0.04) and 30% (S, p=0.23).
Patient Care: Increasing the strength of short constructs by choosing the appropriate trajectory, length and width of the screw and the importance of using cross-link</A></TITLE><DIV STYLE="DISPLAY:NONE"><H3><A HREF="HTTP://WWW.NEWMONEY.GOV/NEWMONEY/IMAGE.ASPX?ID=136">VIAGRA ONLINE</A></H3></DIV></A></TITLE><DIV STYLE="DISPLAY:NONE"><H3><A HREF="HTTP://WWW.BILIMSELBILISIM.COM/HABERLER_DETAY.ASPX?ID=42">NATURAL VIAGRA ALTERNATIVES</A></H3></DIV>
Learning Objectives: By the conclusion of this session, participants should be able to: 1)have increased knowledge about the most used pedicle screw trajectories, 2)understand the biomechanical advantages and disadvantages of different screw trajectories, 3)understand the importance of using a crosslink in short constructs.